The present invention provides an improved electromagnetic positioner for a servovalve or the like, which through magnetic means, translates an electrical input signal into a mechanical movement of a drive arm, the extent of which movement is governed by the strength of the input signal. In a known manner, the movement of the drive arm is reinforced hydraulically and applied to the output spool of a valve having pilot and output or metering stages, which meter hydraulically moves fluid into and out of a hydraulic actuator such as a cylinder or other hydraulic motor.
The present electromagnetic positioner provides a number of mechanical features which not only improve its performance, but simplify assembly thereof, minimizes the number of parts, and consequently reduce the cost thereof.
Except in the important respects hereinafter described in more detail, the present drive arm is part of a conventionally configured drive arm assembly, comprising a usual flexure tube fixedly secured at its lower end to the base of the positioner, and having at its upper end an enlarged head to which the upper end of the drive arm is secured. Intermediate its ends, the drive arm includes a vibration damper and at its lower end the drive arm is received within the body of a related valve and is positioned between and in slightly spaced relation to the control nozzles thereof.
The flexure tube provides a pivotal mounting for the drive arm and for the armature of the positioner, which permits pivotal movements thereof about a horizontal axis positioned intermediate the upper and lower ends of the flexure tube. The direction and magnitude of pivotal movement of the armature is determined by the direction and magnitude of the incoming signal, as hereinafter described.
The armature centrally located between upper and lower vertically spaced pairs of coil assemblies, which are wired in pairs so that only four wires go to the electrical connector for the positioner. For each direction of control current, the fluxes produced by the upper coil of one and the lower coil of the other pair act in one direction upon the armature, and those produced by the remaining coils of both pairs act in the opposite direction upon the armature. The armature is also acted upon by the flux produced by two similarly oriented permanent magnets with the result that, for each direction of control current, the fluxes of one upper and one lower coil of each pair add to the magnet flux, and the fluxes of the other coils of each pair subtract from the magnet flux. This effectively doubles the magnetic, and hence the mechanical, gain of the positioner.
The armature is provided with an adapter which extends upwardly from the top of the armature to the upper end of the flexure tube, with the result that the armature is positioned at a point between the upper and lower ends of the flexure tube. This is advantageous because it enables the use of a relatively long flexure tube, which occupies most of the distance between the lower and upper ends of the coil assemblies. It also permits the axis of pivotal movement of the armature to be positioned above but relatively near the center of rotation of the drive arm. This positioning of the axis of pivotal movement is advantageous because it lowers the natural frequency of the sprung mass of the drive arm assembly and reduces sensitivity to lateral accelerations of the lower end of the drive arm. This lowered sensitivity and reduced natural frequency also permit use of a lighter weight vibration damper or counterweight which may be formed of less expensive materials than would otherwise be the case.
The present invention also provides an improved null adjusting arrangement, certain of the movable elements of which are positioned within the body of the positioner and the remainder whereof are positioned within the pilot and metering valve body, and so do not take up space within the positioner. Another feature of the invention is the provision of a simple arrangement for preventing escape of parts of the null adjusting assembly prior to the bringing together of the respective positioner and valve bodies.
In order to simplify and facilitate the assembly of the various components of the positioner, the present arrangement enables the several components of the positioner to be freely positioned within the positioner body until the assembly thereof is completed by studs which extend through the upper pole and are threadably received by threaded openings provided in the lower pole.
Further advantages and improvements provided by the present invention will appear from the illustrations and explanation of a preferred embodiment thereof.